Through which agency the infection of Ascaris takes place ?

Options

A. Air
B. Mosquito
C. House fly
D. Contaminated food and water

Answer

### Step-by-Step Solution:

1. **Understanding the Organism**: Ascaris is a parasitic roundworm scientifically known as Ascaris lumbricoides. It belongs to the phylum Nematoda.

2. **Mode of Transmission**: Ascaris does not spread directly from one person to another. Instead, the infection occurs through the ingestion of eggs.

3. **Source of Infection**: The eggs of Ascaris are typically found in feces of infected individuals. When these feces contaminate food or water, the eggs can be ingested by a new host.

4. **Contaminated Food and Water**: The primary agency through which Ascaris infection occurs is through contaminated food and water. This means that if someone consumes food or drinks water that has been contaminated with Ascaris eggs, they can become infected.

5. **Lifecycle of Ascaris**: Once ingested, the eggs hatch in the intestine. The larvae then burrow through the gut wall, enter the bloodstream, migrate to the lungs, and eventually return to the intestine as adult worms.

6. **Symptoms of Infection**: The presence of adult worms in the intestine can lead to symptoms such as abdominal pain, vomiting, nausea, fatigue, weight loss, and malnutrition.

7. **Conclusion**: Therefore, the correct answer to the question is that the infection of Ascaris takes place through **contaminated food and water**.

### Final Answer:
**D. Contaminated food and water**